The effects of a polycrystalline surface layer on the critical resolved shear stress, yield stress and the work hardening rate of tin single crystals has been investigated. The change in these parameters was found to be independent of the thickness of the layer. The results have been interpreted in terms of the inhibition of surface sources and the higher stress level required to initiate interior sources. An exploratory investigation of the flow mechanism in tin was undertaken. Tin single crystals oriented for slip on the (110) [001] slip system were deformed in the temperature range from room temperature to -80°C, with the lower limit of temperature being sensitively dependent on the strain-rate. Twinning was observed to be the mode of deformation below this lower limit. Strain-rate change tests at temperatures from -27°C to R.T. were performed in order to assess the activation energy and activation volume. On the basis of these values, the flow mechanism was postulated to be the non-conservative motion of jogs in screw dislocations. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

M. Tech. Metalurgical Engineering. / A research project was launched to produce zinc/ nickel, zinc/ tin and zinc/aluminium alloys at different concentrations and to test zinc pick-up with the typical steels used in South Africa. Results show that the addition of 0.023% Al and 0.06% Ni in the zinc bath can be successfully used to reduce the zinc pick up of commercial grades of steel. Tin improved quality of coating as compared to pure zinc.